Timken Super Precision Bearings for Machine Tool Applications

Ball Bearings
APPLICATIONS
Workhead and tool spindles are often the most important components
of machine tools. Consequently, to reach the requirements for
spindle speed, work accuracy and finish, selection of the proper size
and type of ball bearings to support these spindles is critical.
Of all the rolling bearing types, super precision ball bearings have
proved to be the best value for the wide variety of machine tool
bearing applications, which cover broad ranges of operating loads,
speeds and lubrication conditions. Duplexed, preloaded, angular
contact bearings with one-piece composition cages have excellent
capacity and provide maximum spindle rigidity. These bearings
are widely used to help machines achieve faster speeds, greater
accuracy, smoother finishes and higher production rates.
Many considerations are involved in the choice of bearings for
precision applications. Among those that influence the performance
of machine tool spindles are the internal geometry of the bearings,
the mounting arrangement, the shaft and housing mounting fits,
the balance and alignment of the rotating parts, and last, but
equally important, the lubrication. While many of these factors
are significant in slow-speed applications, all of them must be
considered for high-speed spindles.
To minimize deflection under load, shafts for machine tool spindles
are designed to have a minimum unsupported length and maximum
cross section. For the same reason, spindle housings are designed
heavy enough to carry the work load. Their cross sections are made
as uniform as possible to reduce stress concentration during uneven
deflection of the frame due to thermal changes. In addition, heavy,
well-proportioned housings can function as sinks to conduct heat
away from ball bearings.
SELECTIVE ASSEMBLY
Under certain conditions, it may be desirable to control fits more
accurately without the added expense of using tighter tolerance
bearings and assembly parts. This can be accomplished by selective
assembly of the bearings, shafts and housings after they are sized
and sorted according to bores and outside diameters. Timken
provides bore and O.D. micron coding as standard practice for super
precision angular contact radial ball bearings. This improved fit-up
at assembly helps to maximize spindle precision.
APPLICATION EXAMPLES
Detailed assembly drawings on the following pages are
representative of successful applications of Timken ® super
precision ball bearings; high-cycle wheel heads; high-speed internal
grinding spindles; super precision workheads; and high-speed
router spindles. Contact your Timken representative regarding any
of your application problems.
SPECIAL REQUIREMENTS
High-speed, grease-lubricated spindles and heavy-precision
workheads requiring unusual rigidity and running accuracy are a
few of the many special problems involving super precision bearings.
These and many other applications generally require design features
that can be reviewed by your Timken representative.
High-Speed Internal-Grinding Spindle
Designed for internal precision grinding, this spindle incorporates
2MM9106WI-CR super precision ball bearings, preloaded by a
coiled helical spring cartridge. Thrust load exerted by the springs
ensures close contact of the balls with the bearing raceways under
all operating conditions. The sealed construction provides highly
effective protection against intrusion of coolant and foreign matter.
Grease is packed and sealed in each bearing prior to assembly.
Operating speed of this spindle is 25000 RPM.
2
C
Fig. 105. High-speed internal-grinding spindle.
TIMKEN MACHINE TOOL CATALOG 137